Degradation of the highly reactive hypervalent trifluoromethylation iodine reagent PhI(OAc)(CF3), which can only be generated in situ with mixing PhI(OAc)(2) and TMSCF3 in the presence of CsF, was studied by ESI-MS and GC-MS combined with F-19-NMR. The important transient intermediate PhICF3+ was determined by ESI-MS, and the major volatile products containing CF3 were identified with the authentic compounds by using GC-MS, such as trifluoromethylbenzene, 2-iodobenzotrifluoride, 3-iodobenzotrifluoride, 4-iodobenzotrifluoride. Meanwhile, more evidences obtained with F-19-NMR were given for such degradation reaction. A possible rapid CF3 radical transfer reaction pathway was proposed to clarify such degradation progress based on the experimental results. Therefore, this study may be helpful in elucidating the intrinsic reactivity of PhI(OAc)(CF3) and the possible competing side reactions caused by such self-degradation pathway.